Blow molding systems generally fall into two categories. The first type of system includes a vertical mold parting plane (called a vertical system). The second type includes a horizontal mold parting plane (called a horizontal system). Systems for forming a hollow body including mold halves fastened to the closing plates and vertical mold parting planes are often used to produce plastic bottles and technical molded parts such as parts having an oblong shape with open ends (e.g., air guide conduits). The length of the parts that can be produced by such systems, however, is limited by various parameters including the weight of the extruded tube (which increases with increasing tube length), the type of the plastic materials forming the tube, and the diameter of the tube, the wall thickness, and other parameters. In particular, such systems are not suitable for producing seamless, oblong pipes, conduits, and similar hollow bodies whose longitudinal axes include sharp and/or multiple bends.
For these reasons, seamless parts are often formed using a horizontal system for forming a hollow body. For example, U.S. Pat. No. 5,030,083 to Kohno et al. shows a system including a tube extrusion device with a robot that receives a tube extruded in a suspended manner from a die and then places the tube in a cavity positioned on a lower horizontal molding portion, which, in turn, is situated on a lower closing plate. In operation the molding portion and the closing plate are moved horizontally to a closing unit, where the mold is closed by lowering an upper horizontal closing plate that carries an upper molding portion. A second carriage is connected to a carriage carrying the lower closing plate. The second carriage carries a second lower closing plate and thereon a second lower molding portion, which are moved in tandem with the first lower molding portion and its associated second closing unit. The first and second molding portions are alternately positioned under the die and their respective closing unit. Although a horizontal system forms seamless, oblong molded parts of varying geometries, it is less economical than vertical systems for producing plastic hollow bodies of large diameters (i.e., large diameters with respect to their lengths).
The present invention is directed to a vertical system for forming a hollow body. The system comprises a machine frame with a tube extrusion device and at least one closing unit including first and second vertical closing plates situated below the die of the extrusion device. The vertical plates are guided in opposite directions against one another such that they can be moved away from and toward one another on horizontal posts. The posts may be mounted on a carriage. The carriage can move the closing unit at a right angle to the direction of movement of the vertical closing plates, from a position under the tube extrusion die to a position under a blowing sleeve.